Message size limits in Exchange 2003

Did you know that there are four separate places where you can set message size limits in Exchange?  If any one of them has a lower size limit than another, then that restriction applies.  So you can set size limits at the following levels:

  • Globally
  • At the connector.  You can configure different message sizes for each connector.
  • at the SMTP Virtual server
  • and at the individal user level

There’s a good example in the KB article which explains how it works and helps to troubleshoot issues and stops you going round and round in circles.  But be aware of the conditions that can prevent message delivery:

In this example, the following size limits have been configured:

The global setting is set to 5 MB.
The Exchange SMTP connector is set to 3 MB.
The SMTP virtual server is set to 4 MB.
The user mailbox setting is set to 2 MB.

Because of these settings, users in the Exchange 2000 or Exchange 2003 organization can send and receive messages that are a maximum of 5 MB. Users can send messages through the connector that are a maximum of 3 MB. All mail that passes through the SMTP Virtual Server (sending or receiving) is limited to 4MB. The individual user, whose mailbox setting is 2 MB, is also limited to sending and receiving messages that are a maximum of 2 MB.